Method of treating tundish

ABSTRACT

A method of treating steel tundish. A first step involves subjecting the tundish to rapid cryogenic refrigeration until the tundish is micro-cracked and cryogenically imbrittled. A second step involves impacting the steel tundish with a force sufficient enough to facture and break apart the cryogenically micro-cracked and imbrittled steel tundish.

FIELD OF THE INVENTION

The present invention relates to a method of treating tundish, so it canbe reused in making steel.

BACKGROUND OF THE INVENTION

In the steel making industry, steel tundish are a byproduct of the steelmaking operation. These rectangular byproducts of the steel makingoperation vary in sizes and weight. They can weigh as much as 60 tons.In order to reclaim these steel tundish, size and weight reduction arenecessary to effectively handle and melt down, steel tundish forreclamation purposes. Currently, an oxygen lancing process is used tocut steel tundish into appropriate sizes. This lancing operation is timeconsuming, has a negative environmental impact and, poses negative heathand safety impact.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method oftreating steel tundish. A first step involves subjecting the tundish torapid cryogenic refrigeration until the tundish is micro-cracked andcryogenically imbrittled. A second step involves impacting the steeltundish with a force sufficient enough to facture and break apart thecryogenically micro-cracked and imbrittled steel tundish.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent fromthe following description in which reference is made to the appendeddrawings, the drawings are for the purpose of illustration only and arenot intended to in any way limit the scope of the invention to theparticular embodiment or embodiments shown, wherein:

FIG. 1 is a side elevation view, in section, depicting a tundish beingplaced in a pit in the ground in preparation for treatment in accordancewith the teachings of the present invention.

FIG. 2 is a side elevation view, in section, depicting the pit andtundish illustrated in FIG. 1, with the pit being covered in preparationfor cryogenic refrigeration of the tundish in accordance with theteachings of the present invention.

FIG. 3 is a side elevation view, in section, depicting rapid cryogenicrefrigeration of the tundish in accordance with the teachings of thepresent invention.

FIG. 4 is a side elevation view, in section, depicting removal of thetundish from the pit after cryogenic refrigeration in accordance withthe teachings of the present invention.

FIG. 5 is a side elevation view, in section, depicting impacting thetundish with a steel ball to fracture and break apart the cryogenicallymicro-cracked and imbrittled tundish in accordance with the teachings ofthe present invention.

FIG. 6 is a side elevation view, in section, depicting impacting thetundish to fracture and break apart the cryogenically micro-cracked andimbrittled tundish in accordance with the teachings of the presentinvention.

FIG. 7 is a flow diagram representation of the method of treating atundish in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred method of treating steel tundish, will now be describedwith references to FIG. 1 through FIG. 7

The method involves a first step of subjecting the tundish to rapidcryogenic refrigeration until the tundish is micro-cracked andcryogenically imbrittled. The Figures sequentially show how this isdone. Referring to FIG. 1, tundish 12 is placed into a pit 14 formed inground 16. Pit 14 is preferred to other types of containers due to thefact that it is relatively inexpensive to excavate a pit and pit 14 canbe made to whatever dimensions may be required to accommodate tundish12. Referring to FIG. 2, pit 14 is covered by a styrofoam cover 18.Referring to FIG. 3, a hose 20 from a liquid nitrogen source (not shown)is inserted through cover 18 into pit 14. Liquid nitrogen is introducedinto pit 14 through hose 20. As the objective is to micro-crack andimbrittle tundish 12, liquid nitrogen is introduced rapidly to provide athermal shock to tundish 12. Referring to FIG. 4, the cryogenicallymicro-cracked and imbrittled tundish 12 is then removed from pit 14.Referring to FIG. 5, steel tundish 12 is then impacted with a forcesufficient enough to facture and break apart the cryogenicallymicro-cracked and imbrittled steel tundish. There are, of course,numerous ways in which this can be done. The preferred way and the waywhich has been selected for illustration in FIG. 5 is by dropping aheavy steel ball 21 onto the cryogenically micro cracked and imbrittledtundish 12 using a crane 22. Alternatively, it could be imbrittledtundish 12 that is dropped from crane 22, as shown in FIG. 6, so thattundish 12 breaks into a number of pieces 24

The preferred method involves subjecting a steel tundish to rapidcryogenic temperatures, to micro crack and imbrittle steel tundish forsize reduction purposes. The cryogenic temperature range starts atapproximately -50 degrees Celsius. It will be understood that the methodworks with a combination of temperature and time. As the temperature ismade colder within the Cryogenic temperature range, the lower thecharpys impact resistance becomes, the more rapid the cryogenictemperature differential between inner and outer surface of steeltundish, the greater the number of micro cracking.

Once steel tundish has been micro cracked and imbrittled, throughcryogenic refrigeration, size reduction and reclamation becomes a verysimple matter. The present invention relates to a method ofcryogenically micro cracking and, imbrittling steel tundish, in order toeffectively fracture and break apart steel tundish for reclamationpurposes. When steel tundish is exposed to rapid cryogenic temperaturesfrom ambient temperatures, outer surface of steel tundish contractswhile inner area remains unchanged, this thermally induced contractiondifferential causes internal stresses high enough to over comes thesteel tundishes, ultimate yield strength, resulting in internally microcracking steel tundish. As the steel tundish is exposed to cryogenicrefrigeration in the cryogenic refrigeration unit, low temperatureimbrittlement occurs and, impact resistances becomes progressively loweras the temperature of the steel tundish becomes lower. Once steeltundish is micro cracked and imbrittled, an impact force is used tofracture and, break apart steel tundish.

The described method of cryogenically micro cracking and imbrittlingsteel tundishs, simplify steel tundish size reduction and, enhancehealth and safety, reduce negative environmental impact and, lower thecost of steel tundish size reduction.

Operation:

Cryogenic Process for Tundish

The details of the method will now be described, in accordance with thedetailed instructions given to on-site personnel, which are embodied inthe flow chart labelled as FIG. 7.

1. Ensure sufficient amount of Ln2.

-   -   Starting values are obtained by recording the pressures and        level on the storage tanks.

2. Inspection of tundish.

-   -   Cryogenic operator measures the size of the tundish to be        treated.    -   From the measurement of the tundish, an estimated weight must be        obtained and recorded.

3. Referring to FIG. 1, Tundish 12 is placed in pit 14.

-   -   One signal person must be used to direct the forklift operator.    -   The signal person will direct the forklift operator to raise the        tundish into the engineered lifting cradle.    -   Once the tundish is resting in the cradle the operator will then        raise the spreader to allow the shackles to be applied.    -   Once the shackles have been applied the operator will raise the        tundish and place it into the Cryogenic chamber.

4. Referring to FIG. 2, Apply cover 18 to Cryogenic chamber.

-   -   Covers are applied evenly, leaving only small openings for        venting.

5. Referring to FIG. 3, liquid nitrogen (Ln2) introduction into pit 14through hose 20.

-   -   The inlet hose is secure to ensure flash back does not occur.    -   Ln2 is then introduced into the chamber at a slow rate to start        then opened to facilitate a substantial flow.    -   Once a two (2) to three (3) foot bath is obtain inside the tank,        the Ln2 is reduce to maintain a sufficient bath level as the Ln2        flashes off.

6. Monitor & Document.

-   -   Operator must record all times and events on each tundish        treatment.    -   Operator must record Ln2 usage.

7. Referring to FIG. 4, tundish 12 is removed from pit 14.

-   -   Tunish is then removed and transported to the reclamation area.

8. Referring to FIG. 5, steel ball 21 is-dropped from a height ontotundish 12, with the impact resulting in tundish 12 splitting intosmaller pieces 24.

-   -   Operator must document time of demolition and number of drops        required to demolish tundish 12.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following the word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one of the elements.

It will be apparent to one skilled in the art that modifications may bemade to the illustrated embodiment without departing from the spirit andscope of the invention as hereinafter defined in the Claims.

1. A method of treating steel tundish, comprising the steps of:subjecting the tundish to rapid cryogenic refrigeration until thetundish is micro-cracked and cryogenically imbrittled; and impacting thesteel tundish with a force sufficient enough to facture and break apartthe cryogenically micro-cracked and imbrittled steel tundish.
 2. Amethod of treating steel tundish, comprising the steps of: placing thetundish in a container; covering the container; introducing cryogenicfreezing into the container and subjecting the tundish to rapidcryogenic refrigeration until the tundish is micro-cracked andcryogenically imbrittled; and impacting the steel tundish with a forcesufficient enough to facture and break apart the cryogenicallymicro-cracked and imbrittled steel tundish.
 3. The method as defined inclaim 2, the container being a pit.
 4. The method as defined in claim 2,the tundish being impacted by a steel ball being dropped from a height.5. The method as defined in claim 2, the tundish being impacted by beingdropped from a height.